Inductor for furnaces and the like



July 4,1933. E. F. NORTHRUP 1,916,434

INDUGTOR FOR FURNACES AND THE LIKE- Fi1ed,July 17, 1930 w a i255. y IEIIIE Patented July 4, 1933 UNITED STATES PATENT OFFICE EDWIN rrrcn NOa'rnRUr, or- PRINCETON, NEW annsnx assmnon To'AJAx ELEC- 'rnornnmno CORPORATION, or AJAxrAnK, "NEW JERSEY, A CORPORATION or NEW JnBsEY I Application filed July 17,

My invention relates to' the construction of 1 electric induction furnaces, particularly coreless furnaces, and to methods of heating using such furnaces.

A purpose .of my invention is to supplyinduced current to large induction furnaces evenly along the length of the furnaces without the necessity of connecting a plurality of turns or groups of turns electrically in parallel. i

A further purpose is to construct an inductor coil suitable for heating billets to a forging temperature.

' 'A further purpose is to 'heat-acharge by passing current about it over a relatively wide spiral. path.

A further purpose is to wind an inductor coil fiatwise about the furnace crucible, adjusting the axial dimension. of the individual turns so that a small predetermined number of turns will completely surround the crucible.

A further purpose is to wind an inductor coil from a metallic ribbon or strip of shorter cross sectional dimensionflin one direction than 1n another d1rect1on, placing the shorter cross sectional dimension transverse to the coil axis.

A further purpose is to construct an electric inductioncoil from flattened flatwound tubing, desirably cooling the tubing by passing a suitable medium through its interior from connections.

- fication an a of one of the turns 0 Further urposes will appear in the specid in the claims.

My invention involves both methods and apparatus by which the methods may be carfled o t... U

In the drawing I illustrate a fewonly of the numerous possible structures by which my invention might beembodied, choosingthem from the standpoint of ease in manufacture, convenience in use and facility in illustration of the principles involved.

' Figure 1 is a vertical central section, large- 3 1y diagrammatic, of a furnace to which y invention .has been applied.

Figure 1a is an enlar ed transverse section f the inductor e il of Figure 1. I

' INDUCTOB FOIR-FURNACES AND THE LIKE 1930. Serial No. 468,551.

Figure 2 is a vertical central section of a 'somewhat-diflerent embodiment of my invention from that shown in Figure 1.

Figure 2a is an enlarged transverse section I of one of the inductor coil turns of Figure 2.

Figure 3 corresponds generally to Figure 2, but shows connections for a coolingme- 1 dium.

Figure4 is a vertical central section of my invention applied to heating a billet.

In the past it has been usual to construct.

increase greatly the size of coreless induction furnaces, and simultaneously to reduce the number-of inductor coil turns about these larger, furnaces. .-Where the axial length of r the furnace is increased or the number of. 7

turns in the inductor coil decreased, or both, the turns will be widely separated.

On account of the skin effect and the tend ency of the current in the inductor" to im prove its coupling with the induced current,

the current-carrying cross section with edgewise winding is very' small, having axially;

but little greater length (because of the bend where there is water. cooling) than the axial cross sectional dimension of the tube. Even where a number of edgewound turns are placed inparallel, the cross section for current-carrying purposes is interrupted by .the insulation.

For larger furnacesa small number of turns only is ordinarily required. -Where edgewise wound turns are used the spacing between the turns becomes excessive and the paths of corresponding induction within the i furnace pool are correspondingly separated and more or less distinct instead of'as is most desirable-,-a substantially uniform band a the winding.

I plan to increase the axial dimension of the individual inductor coil turns so that they ma be wound rather closely, and will still rat er continuously surround the crucible to the height desired without the use of an excessive number of turns.

The same strip or tube which is edgewound to great advantage where a large number of turns is required, I find can be flatwound to secure a maximum of axial coverage per turn and a maximumof current-carrying capacity from the standpoints of skin effect and coupling.

In Figure 1 I show the crucible 10 of any desired form surrounded by an inductor coil 11 su plied with current from the source 12 throug l lines 13 and 14, and desirably having its power factor corrected by a suitable reactance 15.

As better seen in Figure 1a, the individual inductor coil turns are desirably of generally rectangular cross-section, and are wound flatwise, so that the greater dimension, that parallel to the side 16 extends axially with respect to the inductor coil, and the lesser dimension, that parallel to the side 17 extends transversely to the axis.

The number of turns about the crucible for a given flat conductor is, of course, limited by the axial space occu ied by the individual turns and their insul zition, but usually, of course, the number of turns and'the cross section will be preliminarily determined and the fiat strip or flattened tubing will be selected or manufactured accordingly.

Because of the high current values required in large induction furnaces, I prefer the structure of Figure 2 to that of Figure 1,

since the inductor coil of Figure 2 conveniently may be cooled. The general external dimensions of the inductor coil turn, as best seen in Figure 2a, correspond generally to those of the turn shown in Figure 1a. The

coil 11 may be formed of hollow tubing fiat-v tened and flat-wound, that is, wound with the face 16. parallel to the axis of the coil.

Suitable connections may be made to the interior of the inductor coil as seen in Figure 3, where the cooling medium is supplied I at'18 and removed at 19. The cooling medium may be supplied under pressure to increase the cooling capacity.

My invention may be very satisfactorily apin The length 0 the billet is usually consi erablygreater than its cross-sectional dimension, so that, if edge winding of a small number of turns were used, the turns would. be widely spaced, and current wouldbe induced nonuniformly.

In Figure 4 I show a billet 20, resting upon a base 21 and surrounded b an inductor coil 11? of hollow flatwound tu ing. Current is passed through the inductor to heat the billet to the forging temperature.

It will be evident that the current surrounding the charge is conducted through a relatively wide path, so that the induced current will be rather uniformly distributed throughout the charge.

I believe that the best application of my invention will be in coreless induction furnaces of considerable size. However, it is also applicable to other electrical windings, as for example reactors, where it is desired to employ fewer turns per unit axial dimension than have been used formerly.

While I consider that the generally rectangular external cross-section is most convenient, it will be understood that my invention may be embodied in coils having variant cross-sections but in which the general axial dimension is greater than the general transverse dimension.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and be connected to a source of cooling medium' underpres'sure.

EDWIN FITCH NORTHRUP. 

